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  • 1. Tamil Shallow Parser using Machine Learning Approach Dhanalakshmi V1, Anand Kumar M1, Soman K P1 and Rajendran S2 1Computational Engineering and Networking Amrita Vishwa Vidyapeetham Coimbatore, India {m_anandkumar,v_dhanalakshmi, kp_soman} @cb.amrita.edu 2Tamil University, Thanjavur, IndiaAbstractThis paper presents the Shallow Parser for Tamil using machine learning approach. Tamil ShallowParser is an important module in Machine Translation from Tamil to any other language. It is also akey component in all NLP applications. It is used to understand natural language by machine and alsouseful for second language learners. The Tamil Shallow Parser was developed using the new and stateof the art machine learning approach. The POS Tagger, Chunker, Morphological Analyzer andDependency Parser were built for implementing the Tamil Shallow Parser. The above modules givesan encouraging result.IntroductionPartial or Shallow Parsing is the task of recovering a limited amount of syntactic information from anatural language sentence. A full parser often provides more information than needed and sometimesit may also give less information. For example, in Information Retrieval, it may be enough to findsimple NPs (Noun Phrases) and VPs (Verb Phrases). In Information Extraction, Summary Generation,and Question Answering System, information about special syntactico-semantic relations such assubject, object, location, time, etc, are needed than elaborate configurational syntactic analyses. In fullparsing, grammar and search strategies are used to assign a complete syntactic structure to sentences.The main problem here is to select the most possible syntactic analysis to be obtained from thousandsof possible analyses a typical parser with a sophisticated grammar may return. This complexity of thetask makes machine learning an attractive option in comparison to the handcrafted rules.MethodologyMachine learning approach is applied here to develop the shallow parser for Tamil. Part of speechtagger for Tamil has been generated using Support Vector Machine approach [Dhanalakshmi V e.tal.,2009]. A novel approach using machine learning has been built for developing morphological analyzerfor Tamil [Anand kumar M e.tal., 2009]. Tamil Chunker has been developed using CRF++ tool[Dhanalakshmi V e.tal., 2009]. And finally, Tamil Dependency parser, which is used to find syntactico-semantic relations such as subject, object, location, time, etc, is built using MALT Parser[Dhanalakshmi V e.tal., 2011]. 175
  • 2. General Framework and Modules • The general block diagram for Tamil Shallow parser is given in Figure 1. Input Sentenc Tokenization POS Tagging Chunking Morphological Analyzer Format Conversion MALT Parser for Relation Shallow Parsed Figure.1. General Framework for Tamil Shallow Parser• Tamil Part-of-Speech Tagger [Dhanalakshmi V e.tal., 2009]: The Part of Speech (POS) tagging is the process of labeling a part of speech or other lexical class marker (noun, verb, adjective, etc.) to each and every word in a sentence. POS tagger was developed for Tamil language using SVMTool [Jes´us Gim´enez and Llu´ıs M`arquez, 2004].• Tamil Morphological Analyzer [Anand Kumar M e.tal., 2009]: Morphological Analysis is the process of breaking down morphologically complex words into their constituent morphemes. It is the primary step for word formation analysis of any language. Morphological Analyzer was developed using a novel machine learning approach and was implemented using SVMTool.• Tamil Chunker [Dhanalakshmi V e.tal., 2009]: Chunks are normally taken to be non recursive correlated group of words. Chunker divides a sentence into its major-non-overlapping phrases 176
  • 3. (noun phrase, verb phrase, etc.) and attaches a label to each chunk. Chunker for Tamil language was developed using CRF++ Tool[Sha F and Pereira F, 2003].• Tamil Dependency Parser for Relation finding [Dhanalakshmi V e.tal., 2011]: Given the POS tag, Morphological information and chunks in a sentence, this decides which relations they have with the main verb (subject, object, location, etc.). Dependency parser was developed for Tamil language using Malt Parser tool [Joakim Nivre and Johan Hall, 2005].Dependency Parsing using Malt ParserMALT Parser Tool is used for dependency parsing, which uses supervised machine learningalgorithm. Using this tool dependency relations and position of the head are obtained for Tamilsentence. There are 10 tuples used in the training data that can be user define. For Tamil dependencyparsing, the following features are defined and others are set as NULL and are mentioned as ‘_’ in thetraining data format. WordID: Position of each word in the input sentence. Words: Each word in the input sentence. CPos Tag and Pos Tag: Defines the Parts Of Speech of each word. Head: The position of the parent of each word. Lemma: The lemma of the word. Morph Features The Morphological features of the word. Chunk The chunk information of the word. Dependency Relation: The terminology given for each parent – child relation. Sample Training Data 1 அவ _ <PRP> <PRP> 8 <N.SUB> _ _ 2 ைடகைள _ <NN> <NN> 3 <D.OBJ> _ _ 3 வா கி _ <VNAV> <VNAV> 4 <ATT> _ _ 4 சைம _ <VNAV> <VNAV> 6 <VNAV.MOD>_ _ 5த _ <NN> <NN> 6 <NST.MOD> _ _ 6 ேபா _ <VNAV> <VNAV> 8 <V.COMP> _ _ 7 உன _ <PRP> <PRP> 8 <I.OBJ> _ _ 8 ெகா கி றா _ <VF> <VF> 0 <ROOT> _ _ 9 . <DOT> <DOT> 8 <SYM> _ _For Tamil language, a corpus of three thousand sentences is annotated with dependency relations andlabels using the customized tag set (Table.1). The corpus is trained using the MALT Parser tool whichgenerates a model. Using this model the new input sentences are tested. 177
  • 4. S.No Tags Description S.No Tags Description 1 ROOT Head word 5 NST-MOD Spatial Time Modifier 2 N-SUB Subject 6 SYM Symbols 3 D-OBJ Direct Object 7 X Others 4 I-OBJ Indirect Object Table.1 Shallow Dependency TagsetApplication of Shallow ParserShallow parsers were used in Verbmobil project [Wahlster W, 2000], to add robustness to a largespeech-to-speech translation system. Shallow parsers are also typically used to reduce the search spacefor full-blown, `deep parsers [Collins, 1999]. Yet another application of shallow parsing is question-answering on the World Wide Web, where there is a need to efficiently process large quantities of ill-formed documents [Buchholz and Daelemans, 2001] and more generally, all text mining applications,e.g. in biology [Sekimizu et al., 1998].The developed Tamil Shallow Parser can be used to develop the following systems for Tamillanguage. • Information extraction and retrieval system for Tamil. • Simple Tamil Machine Translation system. • Tamil Grammar checker. • Automatic Tamil Sentence Structure Analyzer. • Language based educational exercises for Tamil language learners.ConclusionShallow Parsing has proved to be a useful technology for written and spoken language domains. Fullparsing is expensive, and is not very robust. Partial parsing has proved to be much faster and morerobust. Dependency parser is better suited than phrase structure parser for languages with free orflexible word order like Tamil. Fully functional Shallow Parser for Tamil gives reliable results. TheShallow Parser system developed for Tamil is an important tool for Machine Translation betweenTamil and other languages.References Anand kumar M, Dhanalakshmi V , Soman K P and Rajendran S (2009) , “A Novel Approach for Tamil Morphological Analyzer”, Proceedings of the 8th Tamil Internet Conference 2009, Cologne, Germany. Buchholz Sabine and Daelemans Walter (2001), “Complex Answers: A Case Study using a WWW Question Answering System”, Natural Language Engineering. Collins M (1999), “Head-Driven Statistical Models for Natural Language Parsing”, Ph.D Thesis, University of Pennsylvania. 178
  • 5. Dhanalakshmi V, Anand Kumar M, Vijaya M S, Loganathan R, Soman K P, Rajendran S(2008), “Tamil Part-of-Speech tagger based on SVMTool”, Proceedings of the COLIPSInternational Conference on natural language processing(IALP), Chiang Mai, Thailand.Dhanalakshmi V, Anand kumar M, Soman K P and Rajendran S (2009), “POS Tagger andChunker for Tamil Language”, Proceedings of the 8th Tamil Internet Conference, Cologne,Germany.Dhanalakshmi V, Anand Kumar M, Rekha R U, Soman K.P and Rajendran S (2011), “Datadriven Dependency Parser for Tamil and Malayalam” NCILC-2011, Cochin University ofScience & Technology, India.Jes´us Gim´enez and Llu´ıs M`arquez.(2004) SVMTool: A general pos tagger generator based onsupport vector machines.In Proceedings of the 4th LREC Conference, 2004.Joakim Nivre and Johan Hall, MaltParser: A language-independent system for data-drivendependency parsing. In Proceedings of the Fourth Workshop on Treebanks and LinguisticTheories (TLT), 2005.Sekimizu T, Park H and Tsujii J (1998), “Identifying the interaction between genes and geneproducts based on frequently seen verbs in Medline abstracts”, Genome Informatics,Universal Academy Press.Sha F and Pereira F (2003), “Shallow Parsing with Conditional Random Fields”, Proceedingsof Human Language Technology Coference’2003, Canada.Wahlster W (2000), “VERBMOBIL: Foundations of Speech-to-Speech Translation”, Springer-Verlag. 179